It is common practice in service stations and elsewhere to use underground tanks to store petroleum products. The use of such tanks results in greater space utilization as well as greater safety to operators and the public in general. However, the use also has several drawbacks, which include the need to clean the tanks and to remove contaminants which invade and accumulate in the tanks.
Contaminants such as water and sediment tend to accumulate in the bottom of underground storage tanks after a period of use. In some cases, contaminants may be introduced into a tank along with the petroleum product that is put into the tank. Again, when a product is stored in a tank for a long period of time, sediment may grow in the tank in the form of fungus or algae. Further, sediment in the form of metallic scale or rust may fall into the bottom of a tank from the internal sides of the vessel as a result of oxidation or corrosion. Generally, an accumulation of contaminants in a tank will lower the quality of the product stored in the tank. The water and sediments which accumulate in the bottom of a hydrocarbon storage tank are sometimes referred to as bottom sediment and water.
Removal of water in tanks storing fuels which contain alcohols in especially critical because of the affinity of alcohols to water. If the water is not removed, a phase separation is likely to occur in which the alcohol drops out of the fuel because of its attraction to the water phase. A low octane hydrocarbon phase then remains above the water/alcohol phase.
One popular system ("TANKLEENOR") for removing contaminants from underground storage tanks is manufactured and sold by the Gorman-Rupp Company of Mansfield, Ohio. This system includes a hose reel assembly for extending a suction hose into the underground tank, a centrifugal pump attached to the hose assembly, and an operating/discharge barrel for holding fluid for operation of the centrifugal pump and for receiving fluids or other materials withdrawn from the tank. The hose reel assembly is the same as or similar to that shown in U.S. Pat. No. 3,341,880 and includes a rigid guide tube which extends vertically into the underground tank and reaches the bottom of the tank. A flexible hose is stored on a reel and, when in use, is extended through the guide tube to the bottom of the tank at which point the flexible hose turns approximately 90.degree. and extends along the bottom of the tank. A stiffener on one edge of the flexible hose causes the hose to bend in one direction only and the direction of extension of the hose along the bottom of the tank may thus be controlled.
The centrifugal pump used in the TANKLEENOR system takes suction from the operating fluid (usually water) in the operating/discharge drum and discharges the fluid through an eductor in the pump. This discharge of fluid through the eductor creates a vacuum of approximately 16 to 18 inches mercury. The discharge of the eductor is routed back to the metal drum to be once again used by the pump. The flexible hose extending into the underground tank is connected to the vacuum side of the eductor on the centrifugal pump. The vacuum created by discharge of operating fluid through the eductor causes a suction to be applied to the flexible hose. As contaminant is pulled from the tank bottom, it passes into the eductor and joins the eductor operating fluid which is flowing back to the operating/discharge drum. The drum gradually fills with the mixture of the operating fluid being circulated and the contaminant being removed from the tank bottom.
In the TANKLEENOR system and systems similar thereto, the only means for determining flow and for assessing the appearance of the contaminant is a small sight glass on the hose reel. It is not possible to take a sample of the contaminant, because it is under vacuum until it reaches the eductor where it is then mixed with water or other operating fluid. Moreover, the rate of suction of contaminants or product from the underground storage tank may not be regulated because the vacuum created at the eductor is constant. Also, existing systems generally involve the use of an open drum of fluids which include gasoline or other flammable fuels. Finally, the large size and weight of the centrifugal pump required (commonly, 80 gallons per minute capacity) is disadvantageous.